The present invention relates to a process for stabilizing a silicon-containing methacrylate, and more particularly to a process for stabilizing a silicon-containing methacrylate having the formula (I): ##STR2## wherein X is Si(OCH.sub.3).sub.3, Si(OCH.sub.3).sub.2 CH.sub.3, Si(OCH.sub.3)(CH.sub.3).sub.2 or Si(CH.sub.3).sub.3 which comprises adding 2,5-di-t-butylbenzoquinone to the silicon-containing methacrylate, whereby polymerization of the silicon-containing methacrylate can be inhibited.
In case that methacrylates are separated, concentrated or purified, distillation step is generally employed. However, it has been known that methacrylates have a property that methacrylates per se are very easy to polymerize, and particularly, the property is increased when methacrylates are treated at high temperature and are in vapor state as in distillation step. Therefore, a great attention must be given for inhibiting polymerization of methacrylates.
It has been recognized that the stability of a silicon-containing methacrylate represented by the formula (I), particularly methacryloyloxypropyltrimethoxysilane represented by the formula: ##STR3## having a hydrolyzable silicone group such as trimethoxysilyl group and bonding to ester group, is the lowest among various known methacrylates. In case that the silicon-containing methacrylate having the formula (I) which has excellent polymerizable property is industrially prepared, it is very important that a trouble caused by polymerizing the silicon-containing methacrylate is inhibited in distillation step. Particularly, it is necessary and essential that the substantial inhibiting technique in polymerization of the silicon-containing methacrylate is established in order to operate continuously and stably in distillation step.
Examples of the polymerization inhibitor generally employed for methacrylates are, for instance, p-benzoquinone, hydroquinone, p-methoxyphenol, and the like. When methacrylates are distilled, however, the effect of stabilizing methacrylates is not so high as is expected in the above polymerization inhibitors. And further, when the silicon-containing methacrylate, particularly methacryloyloxypropyltrimethoxysilane is distilled, the above polymerization inhibitors are not industrially employed since the above polymerization inhibitor has substantially no effect of inhibiting polymerization of the silicon-containing methacrylate.
An object of the present invention is to provide a process for stabilizing the silicon-containing methacrylate having the formula (I) by adding the suitable polymerization inhibitor to the silicon-containing methacrylate, whereby polymerization of the silicon-containing methacrylate can be inhibited.
The present inventors have found a polymerization inhibitor having an excellent effect of inhibiting polymerization of the silicon-containing methacrylate having the formula (I), particularly methacryloyloxypropyltrimethoxysilane, in comparison with conventional polymerization inhibitors in distillation step.